534 Self-purification of Waters and Soils. [September, 
disregarded, however. Now we must regaid the entiie 
question of self-purification as removed from the field o 
pure chemical research. . . , , , 
Even when industrial refuse of various kinds has been 
allowed to flow into a river, in addition to ofg anl ° P° : “S’ 
it has been again and again demonstrated that selt-punfica 
on can Indies take place. But praaically speakmg we 
must beware of supposing that the treatment of foul waters 
should be left to Nature.. Where the supply of po but g 
matter is continuous in time and space, natu a p > & 
ag Dr C . ie j. f Soyka has almost simultaneously been engaged 
with a series of experiments on the power of the soil to 
absorb poisonous substances from the soil, and to desti y 
them. Solutions of strychnine sulphate, hydrochlorate and 
acetate of different strengths were filtered through i a .cylin- 
drical stratum of gravelly soil, 32 inches in depth, 55 g 
measures of the solution being poured on daily. Attei 
soil had received a quantity of the solution coiiespond g 
to its capacity for water, the excess drained away bu ^ P® 1 " 
fectly free from strychnine. The size of the granule 
travel had no perceptible influence. . 
The addition of strychnine solutions was then repeate 
until the soil was. no longer able to retain stryd^nme. 
was then found that the gravelly soi was able to withdi 
from solution 0-5 to o*6 per cent of its weight of a strych- 
nine salt, and 0-4 per cent of its weight of pure strychnine. 
A similar result was obtained with quinine, morphine, 
atropine, pyridine, piperidine hydrochlorate, cinchonine sul- 
Pl Ttls a much to°be regretted that the author did not consider 
it necessary— or perhaps had not the opportunity— to repeat 
these experiments with any of the ptomaines, bodies muc 
more likely to occur in soils, and whose elimination is, undei 
certain circumstances, of fio small sanitary importance 
The more gradually the poisons are incorpoiated with the 
soil the more of them is retained. The soil, howevei, de- 
composes the salts which it withdraws from solution. T his 
decomposition takes place quantitatively. 1 he acid le- 
appears in the filtrate, whilst the alkaloid remains in the 
sofi and for a time unchanged. Both chemical analysis 
and’ physiological experimentation prove that it is not de- 
The subsequent destiny of the absorbed alkaloids was 
determined by experiments carried on for some months. 
When the soil, saturated with the alkaloid, let the solution 
